The present application relates to a battery pack and a method of calculating the deterioration level thereof, in particular, to a battery pack that allows the deterioration level of a battery to be calculated.
In recent years, as portable electronic units have been widespread, there has been a need for large-capacity and light-weight secondary batteries. As an exemplary secondary battery that satisfies such a need, a lithium ion secondary battery that uses lithium as an electrode reactive substance has become attractive in the field.
When a lithium ion secondary battery becomes deteriorated, its operation time becomes short. Thus, it is desired to calculate the deterioration level of a battery and indicate the calculated result. As an exemplary method of calculating the deterioration level of a battery, which satisfies such a demand, the charging of the battery is turned off, its open circuit voltage is measured, and then its deterioration level is calculated based on the open circuit voltage. This method is disclosed for example in Japanese Patent Application Laid-Open No. 2001-228226 (referred to as Patent Document 1).
However, since the open circuit voltage does not become stable in such a method, it is difficult to accurately calculate the deterioration level of the battery. As factors that cause the open circuit voltage of the battery to fluctuate, it is likely that there are for example ambient environment and resistance of the connection portion. Thus, if the charging off time is increased, the open circuit voltage may become stable. As a matter of practice, however, if the charging stop time is long, the charging time would become long.